This subject matter disclosed herein relates generally to measurement devices, and more particularly to soft-field tomography systems.
Soft-field tomography, for example, Electrical Impedance Spectroscopy (EIS), also referred to as Electrical Impedance Tomography (EIT), is used to measure the internal properties, in particular, the electrical properties of materials of internal structures of an object, such as a region of a human body. Such EIS systems estimate the conductivity and/or permittivity of the materials within a volume based on current and voltage data acquired proximal a surface of a volume. For example, in a human body, the electrical properties are different for air, muscle, fat and other tissues. Moreover, the electrical properties within the body region also vary with time. Accordingly, a time-varying map of electrical properties may be formed based on the conductivity distribution within the volume.
A typical EIS system includes a plurality of transducers that may be arranged and positioned proximal a surface of the object to be studied. An excitation, such as electrical currents are applied to the transducers and a measurement device measures responses, such as the voltages at the transducers. The applied excitations and measured responses are processed to create two-dimensional or three-dimensional representations of the impedance or conductivity distribution of the object, which represents the internal electrical properties of the object.
Conventional multi-channel EIS systems require highly accurate excitation sources operating from a few hundred Hertz (Hz) to a few hundred kHz that are accurate, for example, to the order of 16-bits on each channel of the system. These excitations are applied to a number of transducers and the responses at each transducer are measured to deduce the impedance distribution within the object. Based on dispersion properties of different types of molecules, the impedance distribution across a spectrum of frequencies can be used to identify the types of molecules in the tissue. However, the use of a highly accurate excitation source on each channel increases the overall complexity of each channel.
Thus, in these conventional EIS systems, higher power requirements and more physical space are needed for the electronics. These conventional systems also have a limited bandwidth, thus limiting the capability of the system to measure higher order dispersion. Additionally, these conventional systems are also affected by variations over time and with changes in environmental conditions (e.g., temperature).